A Bangladesh court has sentenced two students to death for the 2013 murder of a secular blogger, delivering the first convictions over a series of such killings that have rattled the Muslim-majority nation.

Police say the banned Islamist group Ansarullah Bangla Team is behind the attacks.

Mr Haider, an architect, became a target of the group after he helped launch a massive protest against the leaders of the largest Islamist party, several of whom are accused of war crimes during Bangladesh's 1971 independence struggle against Pakistan.

Police said Mr Haider, better known by his Bengali online identity Thaba Baba, also wrote against Islam and mocked Prophet Mohammed on blog sites, earning the students' wrath.

They said Rahmani had preached that it was legal to kill atheist bloggers who campaigned against Islam.